Turntable system with low aggregate resonance

ABSTRACT

A high fidelity turntable system with low aggregate resonance is disclosed. The turntable system comprises a tone arm assembly and a belt-driven platter assembly joined rigidly by a silent substructure of pure aluminum tubing. This low acoustic mass substructure is internally damped beyond its resonance point and is resiliently suspended from a base plate in a mounting cabinet to isolate the turntable system from substantially all resonant feedback. The acoustic mass of the turntable system and, consequently, the resonance, is further reduced by decoupling the tone arm counterweight from the tone arm assembly by means of additional resilient elements.

BACKGROUND OF THE INVENTION

The invention pertains generally to high fidelity turntable systems andis more particularly directed to a low aggregate resonance substructurefor mounting such systems.

Turntable designers in the past have exerted much concentration onreducing acoustic distortions in high fidelity systems. Their effortshave primarily been directed to decreasing such distortions as wow andflutter, which are speed inconsistencies, or rumble, which is the basicnoise level inherent in the rotating motion of a system that is receivedby a phonographic cartridge during play. So much success has beenachieved in alleviating these two distortions that they have virtuallybeen eliminated as problems to the serious audiophile.

One acoustic distortion problem for which much less progress has beenmade is resonance. This serious distortion can be described andsummarized as the sounds produced by the substances of which theturntable system is constructed. Further, depending upon the acousticand mechanical coupling of the turntable to its environment, thesesubstances may also include the objects on which the turntable ismounted or even resting. The resonant sounds produced by thesesubstances are created by and amplified along with the musical or otherinformation that the phonographic cartridge is processing, therebyproducing distortion. The problem usually manifests itself as a "thump"or a loss of fidelity in the lower, or even middle, frequencies and issometimes referred to as "one note bass".

Generally, the cause of the problem is accepted as being one offeedback, as the turntable substances will not make sounds bythemselves. Thus, it is the excitation of these substances by the soundsystem itself which produces the resonance and consequent distortion.

It is believed that there are three principal feedback paths in aturntable system. The first is through the air from the acoustic energyproduced by the speakers to the turntable. Energy in the form of soundvibrations excite the turntable system construction through thisacoustic path to produce a resonant distortion.

The second principal path is a mechanical one whereby the mechanicalvibrations of the speakers and the vibrations caused by their acousticalenergy in other surrounding objects are coupled back through any solidobject in contact with the mounting structure of the turntable. Thecloser the speaker is to the turntable system and the more direct themechanical coupling, the more distortion this feedback path creates.

The third path which has not been previously compensated or described isan inherent feedback path where the actual sound vibrations produced bythe cartridge transducing the stylus motion into electrical signalsprovide an excitation for the resonant substances comprising theturntable.

Generally, the prior art has attempted to solve these resonance problemsby providing a very high mass structure for mounting the turntableassembly and by decoupling this high mass structure from the environmentwith resilient members such as springs. The high mass structure willrequire more acoustic energy to resonate and, thus, will alleviate theacoustic feedback while the decoupling springs will isolate the highmass structure from mechanical vibration and substantially limit themechanical feedback.

The high mass of the turntable supporting structure, however, mayexacerbate the inherent feedback as there is a greater amount ofphysical material present to be heard by the tone arm assembly. Further,a massive mounting structure is bulky to handle and necessitates astronger and more expensive set of decoupling springs.

In addition, many modern amplification systems have equalization factorswhere lower notes are amplified more than higher notes. This is tocompensate the method used for the mechanical recording medium wherelower notes produce less physical movement of the stylus and, thus, lesssignal. Lower resonant tones will, consequently, be amplified, alongwith low note information, more than the higher resonant tones. Itwould, therefore, be highly desirable to eliminate as much of the lowresonant feedback from a turntable system as possible, even to theextent of increasing the high resonant tones.

SUMMARY OF THE INVENTION

Therefore, it is a primary object of the present invention to alleviatethese problems found in the prior art and more fully compensate aturntable system for all three feedback paths.

Another object of the invention is to provide a rigid, low resonanceconnecting substructure for the tone arm assembly and the platterassembly of a high fidelity turntable.

A further object of the present invention is to provide a tone armassembly in which the counterweight mass is decoupled acoustically fromthe tone arm.

Still another object of the invention is to provide a rigid, quietsubstructure which is mechanically decoupled from the mounting structureof the turntable assembly.

In accordance with the above-stated objects of the invention there isprovided a turntable system having a platter assembly and tone armassembly connected by a substructure comprising three tubular strutsradially outreaching from the platter assembly rotation axis.Preferably, the tubular substructure is constructed of a material whichhas a high strength-to-mass ratio and is an acoustic substance. In thepreferred embodiment, this acoustic substance is pure aluminum tubingwhich is resonant at frequencies in the high audio range with highertonal qualities and harmonics. Such a substance is easily damped beyondits resonance point by an internal damping substance. In theimplementation shown, a dense foam rubber is packed tightly inside eachsupporting strut for such damping.

In this manner, any acoustic or inherent feedback received by the lowmass structure is damped by the foam rubber and the system reliablyquieted by this method. The low mass substructure is also not resonantto low acoustic notes and low inherent notes and, therefore, they arenot over-simplified or heard. The higher notes that would be heardwithout the internal damping of the supporting structure are easilydissipated by the provision of the internal damping substance.

Further, the counterweight of the tone arm assembly is acousticallydecoupled by resilient means to provide more inherent feedbackdecoupling. The counterweight mass, if isolated from the system, willnot be heard and will produce an even quieter system.

The substructure is resiliently mounted by extension springs from a baseplate of a mounting cabinet to decouple the system from any mechanicalor inherent feedback loop. The extension springs are more effectivedecouplers than compression springs due to the ability of the system touse a lower spring rate and can be further provided with internal foamrubber damping in their flexible, resonant coils. In this manner, theturntable system floats on the three struts of the substructure and allthree feedback paths have been effectively damped or decoupled.

The rigid connection between the platter assembly and tone arm assemblyis important for the fidelity of the reproduction of the information onthe recording disk. Distortion or loss of information can be introducedinto the system if the tone arm assembly, and, thus, the cartridge,moves in a dissimilar mode to the platter assembly or recordedinformation. The present substructure, therefore, provides a rigidconnection necessary for coupling these assemblies without introducingresonant distortion.

These and other objects, features, and advantages of the invention willbe clearer and more fully understood from a reading of the detaileddescription when taken in conjunction with the appended drawingswherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the preferred embodiment of a turntablesystem constructed in accordance with the invention;

FIG. 2 is a longitudinal cross-sectional side view along section line2--2 of FIG. 1;

FIG. 3 is a cross-sectional end view along section line 3--3 of FIG. 1;

FIG. 4 is a fragmentary perspective view of a typical suspensionmounting for the system illustrated in FIG. 1; and

FIG. 5 is a cross-sectional view along section line 5--5 of thecounterweight illustrated in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 and 2, there is shown a high fidelity turntablesystem comprising a tone arm assembly 6 and platter assembly 4 rigidlyconnected by a substructure 8. The tone arm assembly 6, which has aphonographic cartridge 9 cantilevered on the tone arm 10 and balanced bya counterweight 38, is for providing an electrical signal representativeof the mechanical motion of a stylus on a recording surface, as isconventional in the art. The electrical signals pass through connectingwires from the cartridge to a connector 15 and may be then transmittedto an amplifier. Preferably, tone arm assembly 6 is commerciallyavailable as a SME Model 3009, Series III.

A mounting pillar 17 is upwardly standing in a rectangular plate 19which is balanced on a pair of U-shaped mounting members 14 and 14',respectively. Each of the mounting members 14, 14' (as better seen inFIG. 3) are tubular and bent into the U-shape by suitable means to formtwo arms which have affixed at each end a mounting block 12, 12' whichare adapted to receive screws through drilled apertures in therectangular base plate 19. Grommets 2, 2' are inserted in the aperturesbetween the plate and screws to break one part of the feedback pathbetween the base plate and the substructure by sitting on the mountingblocks and isolating the connecting structure from the U-shaped mountingmembers.

Each of the U-shaped mounting members, 14, 14', are connected to a maintubular support strut 20 by means of a single metal screw 21, andconventionally fixed by a nut.

The main tubular support strut 20 extends to a point beneath the platterassembly 4 where it is connected to a disk-shaped plate 25, preferrablywith two small metal screws. The plate 25 also has mounted, in a smilarmanner by two small screws, tubular struts 24, 24' which connect at anangle to provide an equiangular mounting structure. The three struts areequal angularly provided as radial extensions from the rotational axisof the platter assembly 4 for balance and, with the least number ofsupport elements.

The struts are preferably constructed of an acoustic material that has avery high strength-to-mass ratio so they may provide a low resonancestructure with adequate structural support. The struts, being tubular,are closed upon themselves and have no open vibratory surfaces. Thus,vibrations will be transmitted along the longitudinal axis of the strut.Each tubular strut is provided with an internal damping material 64 (seeFIG. 4), preferably dense foam rubber, that will quickly dissipatevibrations and resonances that are excited in the material. In thisimplementation very pure aluminum tubing is utilized and the high tonalqualities and harmonics that might be excited and transmitted in thissubstance are easily damped out and not heard by the tone arm. Thus, arigid substructure that has a low aggregate resonance has been shown inaccordance with one of the objects of the invention.

Each tubular strut is isolated from the mechanical and inherent feedbackpath by an extension spring 34, 36, 33 (see, for example spring 34 inFIG. 4). The struts are decoupled from a base plate 37 by hooking oneend of the extension spring 34 over an eyelet 35 screwed into the plate,and the other end of the spring through a drilled hole in the end of thetubular strut 20. The base plate 37 mounts in a peripheral ridge in amounting mounting cabinet 32 to allow the system to float free ofmechanical disturbances.

Because of the lower mass and resonance of the substructure 8, lessresilient springs must be used. Also, the springs can be provided asextension rather than compression springs which will produce even moreeffective decoupling of the mechanical feedback path. A naturaloscillation frequency of approximately 2-3 Hz. will produce the mosteffective decoupling and the springs may further be damped internallywith a dense foam rubber material.

The lower the frequency of the oscillation of the mass and springcombination, the greater will be the decoupling. The decoupling iseffective when between the natural frequencies of the platter assemblyand the tone arm assembly which are generally 8 Hz. and 1.5 Hz.,respectively.

The platter assembly 4 is positioned on the top side of the disk plate25 by three hexagonally-headed mounting bolts 30. The connection isisolated from the substructure by wrapping dense foam rubber 22, 22'around the mounting screws. In this manner, the screws are not allowedto touch the platter assembly. This creates a mild but effectiveacoustic barrier for the transmission of vibration through the systemand quiets part of the inherent feedback path. The hexagonal heads onthe screws 30 are used to facilitate balancing and leveling the mountingwith a wrench once the platter is assembled and placed in position.

The platter assembly 4 comprises the base plate 25 screwed to a mountingplate 26 having an upwardly standing spindle 37 which has a bearingassembly for mounting a drive wheel 42, onto which a disk-shaped platter44 may be placed. The platter assembly 4 sans the disk plate 25 was acomponent of an ERA MK6C Turntable.

The drive wheel 42 is operably driven by a flexible belt 41 that isslipped over the drive shaft of a vertically mounted motor 62 on anacoustic base 43. The motor 62 may be provided with suitable drivecontrols via connector 60. The flexibility of the drive belt 41contributes to the reduction in resonance and noise, as vibrations fromthe motor are not transmitted readily through the elastic medium to theplatter assembly. The drive pulley fitted on the shaft of the motor 34is supplied with two differently sized tracks so that the drive belt maybe moved into either track depending on the speed selected for therecording.

When the platter 44 is removed, the substructure 8 will be lifted upwardby the extension springs 33, 34, 36 on which it is suspended, andC-shaped holding blocks 50 and 52 are provided cross-wise to the radialstruts to limit this movement. Likewise, a transverse bar 56 limits theupward movement of the main support strut 20. All the limitingstructures 50, 52 and 56 can be equipped with small pads where theycontact the struts of the substructure to prevent damage thereto.

Turning now to FIG. 5, in accordance with one of the objects of theinvention, the counterweight for the tone arm has been decoupledacoustically from the mass of the turntable system by a pair ofextension springs 40 and 40'. The counterweight, as preferably shown, isa cylindrically-shaped weight of the adequate mass to balance the tonearm and provide the correct tracking pressure on a recording surface.The counterweight 38 is center-bored and has extension spring 40, 40'extending through two radial apertures to attach at one end to a dowel39 located transversely within the center bore. The other ends of theextension springs 40, 40' attach over the finger-like projections of thetone arm to apply the counterbalancing force. In this manner the forceof the counterweight is apparent to the tone arm assembly to provide thecorrect tracking pressure, but its mass is not heard by the system.

While the preferred embodiments of the invention have been shown, itwill be obvious to those skilled in the art that modifications andchanges may be made to the disclosed system without departing from thespirit and scope of the invention as defined by the appended claims.

What is claimed is:
 1. A high-fidelity turntable system for reproducinga disc having a sound recording thereon whose frequencies lie in anaudio spectrum extending from a low frequency range to a high frequencyrange, said system comprising:A. a platter assembly for rotating thedisc; B. a tone arm assembly whose arm carries a phonograph cartridgehaving a stylus engageable with the disc to produce signals inaccordance with the sound recording; and C. a low mass substructuresupporting said assemblies in a mounting environment and including amain strut of rigid light-weight material bridging the platter assemblyand the tone arm assembly and having resonance characteristics lyingabove said low-frequency range, said strut having a hollow region withinternal damping material therein functioning to dissipate vibrationsand resonances excited in said strut in the course of turntableoperation whereby said strut is acoustically quiescent throughout saidspectrum and the signals produced by the stylus are substantially thosederived from the sound recording.
 2. A turntable system as set forth inclaim 1, wherein said tone arm assembly is provided with a counterweightand further including means resiliently decoupling the counterweightfrom the tone arm assembly in a manner whereby the mass of thecounterweight is apparent to said cartridge to effect correct trackingpressure therefor but is acoustically decoupled therefrom so that themass is not sensed by the system.
 3. A turntable system as set forth inclaim 1, further including means for decoupling said substructure fromits mounting environment to cause said system effectively to float,thereby reducing mechanical feedback.
 4. A turntable system as set forthin claim 3, wherein said decoupling means is constituted by extensionsprings having a spring rate at which the system has a vibratory modebetween the resonance point of the rotating platter assembly and that ofthe tone arm.
 5. A turntable system as set forth in claim 4, whereinsaid springs cause the system to vibrate below 3 Hz.
 6. A turntable asset forth in claim 4, wherein said substrate further includes at leasttwo acoustically-quiescent auxiliary struts comparable in structure tosaid main strut, said auxiliary struts, and said main strut radiatingfrom the axis of rotation of said platter assembly and being connectedat their distal extensions by said springs to said mounting environment.7. A turntable system as set forth in claim 1, wherein said main structis acoustically damped by dense foam rubber material packed in thehollow region thereof.
 8. A turntable as set forth in claim 1, whereinsaid main strut is formed by tubing of pure aluminum tubing which isnon-resonant in said low-frequency range.
 9. A turntable system as setforth in claim 1, wherein said tone arm assembly is provided with amounting plate having four corners and is connected to said main strutby a pair of U-shaped tubular mounting members, the arms of one memberbeing connected to two of said corners and the arms of the other memberbeing connected to the other two corners, the bends of said membersbeing secured to said main strut.
 10. A turntable system as set forth inclaim 1, further including means limiting upward movement of saidsubstructure when a platter is removed from said platter assembly.
 11. Aturntable system as set forth in claim 2, wherein said counterweight iscylindrical in form and has a center bore, said counterweight beingresiliently decoupled from the tone arm assembly by a pair of extensionsprings.
 12. A turntable system as set forth in claim 11, wherein saidcounterweight is mounted by affixing one end of each extension spring toa dowel in said center bore and the other end thereof to said tone arm,said extension springs passing through apertures in said counterweight.13. A turntable system as set forth in claim 9, further includingdecoupling means interposed between each arm of said U-shaped mountingmembers and said mounting plate for acoustically decoupling said tonearm assembly from said substructure.
 14. A turntable as set forth inclaim 6, further including decoupling means interposed between saidplatter assembly and said struts for acoustically-decoupling saidsubstructure from said platter assembly.